The dynamics of water within a nanopool of a reverse micelle is heavily affected by the amphiphilic interface. In this work, the terahertz (THz) spectra of cyclohexane/Igepal/water nonionic reverse micelle mixture are measured by THz time-domain spectroscopy and analyzed with two Debye models and complex permittivity of background with volume ratios. Based on the fitted parameters of bulk and fast water, the molar concentration of all kinds of water molecules and hydration water molecule number per Igepal molecule are calculated. We find that slow hydration water has the highest proportion in water when the radius parameter , while bulk water becomes the main component when . The feature radius ratio of nonhydrated and hydrated water to total water nanopool is roughly obtained from 0.39 to 0.85 with increasing .reverse micelle water dynamics THz spectroscopy
Chinese Optics Letters
2024, 22(1): 013001
The distribution of metal nanoparticles on the surface of a surface enhancement Raman scattering (SERS)-active substrate plays a prominent part in not only the enhancement of Raman vibration signal, but also the spectrum uniformity. Here, a facile method to fabricate SERS substrates with excellent homogeneity and low cost was proposed, in which a lyotropic liquid crystal soft template was introduced for the coordinated growth of the silver nanoflowers in the process of electrochemistry deposition. Simulation was carried out to illustrate the dominated influence of the distance of electrodes on the deposited nanoparticle number. Two kinds of conductive materials, silver plate and indium tin oxide (ITO) glass, were chosen as the anode, while the cathode was fixed as ITO glass. The simulated conjecture on the effect of electrode flatness on the uniformity of deposited nanoparticles in silver is experimentally proved. More importantly, it was demonstrated that with a relatively smooth and flat ITO glass anode, a SERS substrate featuring higher spectrum uniformity could be achieved. This work is of great significance to the actual applications of the SERS substrate for quantitative detection with high sensitivity.SERS Raman spectrum surface flatness nanoparticle distribution electrodeposition
Chinese Optics Letters
2023, 21(11): 113001
Laser absorption spectroscopy (LAS) has been widely used for unambiguous detection and accurate quantification of gas species in a diverse range of fields. However, up-to-date LAS-based gas sensors still face challenges in applications where gas concentrations change in a wide range, since it is extremely difficult to balance spectral analysis strategies for different optical thicknesses. Here we present laser vector spectroscopy that combines absorption spectroscopy with dispersion spectroscopy, simultaneously taking advantage of the former’s high sensitivity in the low-concentration region and the latter’s high linearity in the high-concentration region. In the proof-of-concept demonstration of acetylene measurement, it achieves a linear dynamic range of (), which surpasses all other state-of-the-art LAS techniques by more than an order of magnitude, with the capability of highly accurate quantification retained. The proposed laser spectroscopic method paves a novel way of developing large-dynamic-range gas sensors for environmental, medical, and industrial applications.
2023, 11(10): 1687
Dual-comb spectroscopy (DCS) has revolutionized numerous spectroscopic applications due to its high spectral resolution and fast measurement speed. Substantial efforts have been made to obtain a coherent dual-comb source at various spectral regions through nonlinear frequency conversion, where the preservation of coherence has become a problem of great importance. In this study, we report the generation of coherent dual-comb sources covering from the ultraviolet to mid-infrared region based on high-order harmonic generation. Driven by high-repetition-rate femtosecond mid-infrared dual-comb pump pulses, up to ninth-order harmonic was generated from the ultraviolet to mid-infrared region using an aperiodically poled lithium niobate waveguide. To investigate the coherence property of the high-order harmonic generation, DCS was performed at every generated spectral region from 450 to 3600 nm. The measured dual-comb spectra with distinctive tooth-resolved structures show the well-preserved coherence without apparent degradation after the cascaded quadratic nonlinear processes. The subsequent methane absorption spectroscopy at multiple spectral regions of different harmonics was carried out to characterize the spectroscopic capability of the system. These results demonstrate the potential of our scheme to generate compact and coherent broadband optical frequency combs for simultaneous multi-target detections.
2023, 11(8): 1373
This paper investigates the combination of laser-induced breakdown spectroscopy (LIBS) and deep convolutional neural networks (CNNs) to classify copper concentrate samples using pretrained CNN models through transfer learning. Four pretrained CNN models were compared. The LIBS profiles were augmented into 2D matrices. Three transfer learning methods were tried. All the models got a high classification accuracy of , with the highest at 96.2% for VGG16. These results suggested that the knowledge learned from machine vision by the CNN models can accelerate the training process and reduce the risk of overfitting. The results showed that deep CNN and transfer learning have great potential for the classification of copper concentrates by portable LIBS.laser-induced breakdown spectroscopy convolutional neural networks classification flotation concentrate transfer learning
Chinese Optics Letters
2023, 21(4): 043001
Measuring magnetic response from spin and current is of fundamental interest in condensed matter physics. Negatively charged nitrogen-vacancy () centers in diamond are emerging as a robust and versatile quantum sensor owing to their high sensitivity, nanometer-scale spatial resolution, and noninvasive operation with access to static and dynamic magnetic and electron transport properties. In this review, we discuss the rapidly growing interest in the implementation of magnetometry to explore condensed matter physics, focusing on three topics: anti/ferromagnetic materials, superconductors, and metals/semimetals/semiconductors.
2023, 11(3): 393
Exploiting the time-resolving ability of ultrafast pulses, Fourier-transform coherent anti-Stokes Raman scattering (FT-CARS) stands out among the coherent Raman spectroscopic techniques for providing high-speed vibrational spectra with high spectral resolution, high Raman intensity, and immunity to nonresonant background. However, the impulsive stimulation nature of FT-CARS imposes heavy demands on the laser source and makes it inherently difficult to monitor high-frequency vibrations. Here, a novel FT-CARS strategy to our knowledge based on interpulse stimulation is proposed to provide more flexible measuring wavenumber region and lighten the requirement on ultrafast pulses. The mechanism of this technique is analyzed theoretically, and simulation is performed to show an orders-of-magnitude improvement of Raman intensity in the high-wavenumber region by the method. Experimentally, an ytterbium-doped fiber laser and photonic crystal fiber-based solitons are employed to provide two pulses as the pump and Stokes, respectively, and to perform interpulse stimulation FT-CARS without sophisticated dispersion control devices. The high-wavenumber region and upper-part fingerprint region measurements are demonstrated as examples of flexible measurement. Combined with other rapid scanning techniques, such as resonant scanners or a dual-comb scheme, this interpulse stimulation FT-CARS promises to make the fascinating FT-CARS available for any desired wavenumber region, covering many more realistic scenarios for biomedical, pathological, and environmental research.
2023, 11(2): 357
In the field of absorption spectroscopy, the multipass cell (MPC) is one of the key elements. It has the advantages of simple structure, easy adjustment, and high spectral coverage, which is an effective way to improve the detection sensitivity of gas sensing systems such as tunable diode laser absorption spectroscopy. This invited paper summarizes the design theory and the research results of some mainstream types of MPCs based on two mirrors and more than two mirrors in recent years, and briefly introduces the application of some processed products. The design theory of modified ABCD matrix and vector reflection principle are explained in detail. Finally, trends in its development are predicted.multipass cell tunable diode laser absorption spectroscopy gas sensing optical path length
Chinese Optics Letters
2023, 21(3): 033001
Luminescence thermometry can perform noninvasive thermal sensing with high spatial resolution and fast response, emerging as an exciting field of research due to its promising applications in biomedicine. Nevertheless, because of the interaction between light and complex tissues, the reliability and the accuracy of this technique suffer serious interference, which significantly restricts its practical utilization. Here, a strategy to implement effective luminescence nanothermometry is preliminarily proposed by employing the different thermal responses between and energy transfer processes. Different from the traditional ratiometric sensing method, where two luminescence intensities are used as the thermal response parameters, we use two intensity ratios between and near-IR emissions that are obtained under dual excitation as the detecting and reference signals to perform temperature measurement. This multiparameter-based, self-reference thermometry technique, as we define it, exhibits excellent immunity to the influences arising from the fluctuation and loss of pumping sources as well as the luminescence attenuation in media. High thermal sensitivity () and good resolution () are successfully achieved here, accompanied by a measurement error of in a biological environment test, while large errors are observed based on the traditional ratiometric approach (). We believe the viewpoint in this work could boost luminescence thermometry and provide an ingenious route toward high-performance thermal sensing for biological systems.
2022, 10(11): 2532
We present a non-contact optical investigation of laser-induced plasma at moderate Ar pressure ranging from 1 to 100 Pa. The significant shock front and spatial fractionation among the different charged ions are demonstrated at the pressure of 20 Pa. The collisions between Si IV ions and ambient Ar atoms generate distinct and excited Ar II ions, fresh Si III ions, and electrons at the dense layer. The electron density peaks at the position of the shock front, indicating that the collision that yields electrons is dominant over the recombination process in the region of the shock layer and its immediate vicinity.laser ablation moderate pressure shock wave front collision and recombination
Chinese Optics Letters
2023, 21(2): 023001